1. Field of the Invention
The invention relates to a fuel injection nozzle having a nozzle body, a nozzle needle that is displaceable in the nozzle body, a piezoelectric actuator that is connected to the nozzle needle, and a compensation piston on which the piezoelectric actuator is braced and which protrudes into a compensation chamber that is filled with a fluid, wherein the compensation chamber communicates with a supply volume through an inlet of small cross section.
2. Description of the Prior Art
One such injection nozzle is known from German Patent Disclosure DE 35 33 085 A1. The compensation piston makes it possible to compensate for a change in length of the piezoelectric actuator that ensues at low speed. A change in length of this kind is brought about in particular by a change in temperature. If such a change occurs, the fluid is positively displaced by the compensation piston either out of or into the compensation chamber. Conversely, if a rapid change in length of the piezoelectric actuator occurs, as is brought about for opening of the nozzle needle, then because of the small cross section of the inlet, such high resistance to any displacement of the fluid present in the compensation chamber is presented that the compensation piston functions as a rigid abutment. The nozzle needle can then be actuated without the compensation piston having any effect on the resultant opening stroke.
In the known injection nozzle, which is an outward-opening nozzle, a separate restoring spring is provided for the nozzle needle. Opening the nozzle needle requires that the piezoelectric actuator overcome the force exerted by the restoring spring, and this means strong actuation forces.
The object of the invention is to create a fuel injection nozzle that makes do without the restoring spring that has to be overcome by the piezoelectric actuator.
A fuel injection nozzle of the type defined at the outset has the advantage that the pressure prevailing in the supply volume, which also acts on the compensation piston, is comparable to a restoring spring for the nozzle needle, so that a separate, strongly prestressed restoring spring can be dispensed with.